Month: April 2022

Run Code on Spring Startup

@Component
public class EventListenerExampleBean {

    private static final Logger LOG 
      = Logger.getLogger(EventListenerExampleBean.class);

    public static int counter;

    @EventListener
    public void onApplicationEvent(ContextRefreshedEvent event) {
        LOG.info("Increment counter");
        counter++;
    }
}

We can use this approach for running logic after the Spring context has been initialized. So, we aren’t focusing on any particular bean. We’re instead waiting for all of them to initialize.

We want to make sure to pick an appropriate event for our needs. In this example, we chose the ContextRefreshedEvent.

References
https://www.baeldung.com/running-setup-logic-on-startup-in-spring

Configure and Use Spring Data Redis

Configuration

@Configuration
public class RedisConfiguration {

    @Bean
    public LettuceConnectionFactory redisConnectionFactory() {
        ConfigFile configFile = new ConfigFile();
        RedisStandaloneConfiguration configuration = new RedisStandaloneConfiguration(configFile.getRedisHost());
        configuration.setPassword(configFile.getRedisPassword());
        return new LettuceConnectionFactory(configuration);
    }

    @Bean
    public StringRedisTemplate redisTemplate() {
        return new StringRedisTemplate(redisConnectionFactory());
    }
}

You can use RedisTemplate instead of StringRedisTemplate.

Redis Repository

@RedisHash("Student")
public class Student implements Serializable {
  
    public enum Gender { 
        MALE, FEMALE
    }

    @Id private String id;
    private String name;
    private Gender gender;
    private int grade;
    // ...
}

The Spring Data Repository

@Repository
public interface StudentRepository extends CrudRepository<Student, String> {}

Data Access Using StudentRepository

Saving a New Student Object

Student student = new Student(
  "Eng2015001", "John Doe", Student.Gender.MALE, 1);
studentRepository.save(student);

Retrieving an Existing Student Object

Student retrievedStudent = 
  studentRepository.findById("Eng2015001").get();

Updating an Existing Student Object

retrievedStudent.setName("Richard Watson");
studentRepository.save(student);

Deleting Existing Student Data

studentRepository.deleteById(student.getId());

Find All Student Data

Student engStudent = new Student(
  "Eng2015001", "John Doe", Student.Gender.MALE, 1);
Student medStudent = new Student(
  "Med2015001", "Gareth Houston", Student.Gender.MALE, 2);
studentRepository.save(engStudent);
studentRepository.save(medStudent);

References
https://docs.spring.io/spring-data/redis/docs/current/reference/html/
https://www.baeldung.com/spring-data-redis-tutorial

Programmatically Change the Default Port in Spring Boot

@SpringBootApplication
public class CustomApplication {
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication(CustomApplication.class);
        app.setDefaultProperties(Collections
          .singletonMap("server.port", "8083"));
        app.run(args);
    }
}

or

@Configuration
public class ServerPortCustomizer 
  implements WebServerFactoryCustomizer<ConfigurableWebServerFactory> {
 
    @Override
    public void customize(ConfigurableWebServerFactory factory) {
        factory.setPort(8086);
    }
}

References
https://www.baeldung.com/spring-boot-change-port

Configure Spring AMQP to Connect to Multiple Broker

@SpringBootApplication(exclude = RabbitAutoConfiguration.class)
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    CachingConnectionFactory cf1() {
        return new CachingConnectionFactory("localhost");
    }

    @Bean
    CachingConnectionFactory cf2() {
        return new CachingConnectionFactory("otherHost");
    }

    @Bean
    CachingConnectionFactory cf3() {
        return new CachingConnectionFactory("thirdHost");
    }

    @Bean
    SimpleRoutingConnectionFactory rcf(CachingConnectionFactory cf1,
            CachingConnectionFactory cf2, CachingConnectionFactory cf3) {

        SimpleRoutingConnectionFactory rcf = new SimpleRoutingConnectionFactory();
        rcf.setDefaultTargetConnectionFactory(cf1);
        rcf.setTargetConnectionFactories(Map.of("one", cf1, "two", cf2, "three", cf3));
        return rcf;
    }

    @Bean("factory1-admin")
    RabbitAdmin admin1(CachingConnectionFactory cf1) {
        return new RabbitAdmin(cf1);
    }

    @Bean("factory2-admin")
    RabbitAdmin admin2(CachingConnectionFactory cf2) {
        return new RabbitAdmin(cf2);
    }

    @Bean("factory3-admin")
    RabbitAdmin admin3(CachingConnectionFactory cf3) {
        return new RabbitAdmin(cf3);
    }

    @Bean
    public RabbitListenerEndpointRegistry rabbitListenerEndpointRegistry() {
        return new RabbitListenerEndpointRegistry();
    }

    @Bean
    public RabbitListenerAnnotationBeanPostProcessor postProcessor(RabbitListenerEndpointRegistry registry) {
        MultiRabbitListenerAnnotationBeanPostProcessor postProcessor
                = new MultiRabbitListenerAnnotationBeanPostProcessor();
        postProcessor.setEndpointRegistry(registry);
        postProcessor.setContainerFactoryBeanName("defaultContainerFactory");
        return postProcessor;
    }

    @Bean
    public SimpleRabbitListenerContainerFactory factory1(CachingConnectionFactory cf1) {
        SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
        factory.setConnectionFactory(cf1);
        return factory;
    }

    @Bean
    public SimpleRabbitListenerContainerFactory factory2(CachingConnectionFactory cf2) {
        SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
        factory.setConnectionFactory(cf2);
        return factory;
    }

    @Bean
    public SimpleRabbitListenerContainerFactory factory3(CachingConnectionFactory cf3) {
        SimpleRabbitListenerContainerFactory factory = new SimpleRabbitListenerContainerFactory();
        factory.setConnectionFactory(cf3);
        return factory;
    }

    @Bean
    RabbitTemplate template(SimpleRoutingConnectionFactory rcf) {
        return new RabbitTemplate(rcf);
    }

    @Bean
    ConnectionFactoryContextWrapper wrapper(SimpleRoutingConnectionFactory rcf) {
        return new ConnectionFactoryContextWrapper(rcf);
    }

}

@Component
class Listeners {

    @RabbitListener(queuesToDeclare = @Queue("q1"), containerFactory = "factory1")
    public void listen1(String in) {

    }

    @RabbitListener(queuesToDeclare = @Queue("q2"), containerFactory = "factory2")
    public void listen2(String in) {

    }

    @RabbitListener(queuesToDeclare = @Queue("q3"), containerFactory = "factory3")
    public void listen3(String in) {

    }

}

References
https://docs.spring.io/spring-amqp/docs/current/reference/html/#multi-rabbit

Configure Spring AMQP to Receive Messages Asynchronously from Queues

RabbitConfiguration.java

@Bean
public SimpleMessageListenerContainer messageListenerContainer() {
    // configure listener to receive messages from queues
    SimpleMessageListenerContainer container = new SimpleMessageListenerContainer();
    container.setConnectionFactory(connectionFactory());
    container.setConcurrentConsumers(8);
    container.setMaxConcurrentConsumers(32);
    // listen to queues
    container.setQueueNames("MonitoringV5_Queue1", "MonitoringV5_Queue2");
    container.setMessageListener(new RabbitMessageListener());
    return container;
}
public class RabbitMessageListener implements MessageListener {
    @Override
    public void onMessage(Message message) {
        switch (message.getMessageProperties().getConsumerQueue()) {
            case "MonitoringV5_Queue1" -> Queue1(message);
            case "MonitoringV5_Queue2" -> Queue2(message);
        }
    }

    private void Queue1(Message message) {
        String str=new String(message.getBody());
        System.out.println(str);
        Gson gson = new Gson();
        ReadValueDto value= gson.fromJson(str,ReadValueDto.class);
    }

    private void Queue2(Message message) {
        String str=new String(message.getBody());
        System.out.println(str);
        Gson gson = new Gson();
        ReadValueDto value= gson.fromJson(str,ReadValueDto.class);
    }
}

If your callback logic depends on the AMQP Channel instance for any reason, you may instead use the ChannelAwareMessageListener. It looks similar but has an extra parameter.

References
https://docs.spring.io/spring-amqp/docs/current/reference/html/#message-listener

Configure RabbitTemplate to use Spring Retry Policy

@Bean
public RabbitTemplate rabbitTemplate() {
    RabbitTemplate template = new RabbitTemplate(connectionFactory());
    // configure template to use retry policy
    RetryTemplate retryTemplate = new RetryTemplate();
    ExponentialBackOffPolicy backOffPolicy = new ExponentialBackOffPolicy();
    backOffPolicy.setInitialInterval(500);
    backOffPolicy.setMultiplier(10.0);
    backOffPolicy.setMaxInterval(10000);
    retryTemplate.setBackOffPolicy(backOffPolicy);
    template.setRetryTemplate(retryTemplate);
    return template;
}

References
https://docs.spring.io/spring-amqp/docs/current/reference/html/#template-retry
https://www.baeldung.com/spring-retry

Configure Spring AMQP to Connect to RabbitMQ using Credential

@Configuration
public class RabbitConfiguration {

    @Bean
    public CachingConnectionFactory connectionFactory() {
        // configure to connect with credential
        ConfigFile configFile = new ConfigFile();
        CachingConnectionFactory connectionFactory =
                new CachingConnectionFactory(configFile.getRabbitmqHost());
        connectionFactory.setUsername(configFile.getRabbitmqUserName());
        connectionFactory.setPassword(configFile.getRabbitmqPassword());
        return connectionFactory;
    }

    @Bean
    public RabbitAdmin amqpAdmin() {
        return new RabbitAdmin(connectionFactory());
    }

    @Bean
    public RabbitTemplate rabbitTemplate() {
        RabbitTemplate template = new RabbitTemplate(connectionFactory());
        return template;
    }

    @Bean
    public Queue MonitoringV5_Queue1() {
        // declare queue1
        return new Queue("MonitoringV5_Queue1");
    }

    @Bean
    public Queue MonitoringV5_Queue2() {
        // declare queue2
        return new Queue("MonitoringV5_Queue2");
    }
}

References
https://docs.spring.io/spring-amqp/docs/current/reference/html/#cachingconnectionfactory

Generate and Prepare a new GPG key for Github

Generating a GPG key

gpg --full-generate-key
gpg --list-secret-keys --keyid-format=long

From the list of GPG keys, copy the long form of the GPG key ID you’d like to use. In this example, the GPG key ID is 3AA5C34371567BD2:

$ gpg --list-secret-keys --keyid-format=long
/Users/hubot/.gnupg/secring.gpg
------------------------------------
sec   4096R/3AA5C34371567BD2 2016-03-10 [expires: 2017-03-10]
uid                          Hubot 
ssb   4096R/42B317FD4BA89E7A 2016-03-10
gpg --armor --export 3AA5C34371567BD2
# Prints the GPG key ID, in ASCII armor format

Copy your GPG key, beginning with -----BEGIN PGP PUBLIC KEY BLOCK----- and ending with -----END PGP PUBLIC KEY BLOCK-----.

References
https://docs.github.com/en/authentication/managing-commit-signature-verification/generating-a-new-gpg-key